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[ValueTracking] Use Inst::comesBefore in isValidAssumeForCtx (NFC).

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D51664 added Instruction::comesBefore which should provide better
performance than the manual check.

Reviewers: rnk, nikic, spatel

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D76228
This commit is contained in:
Florian Hahn 2020-04-05 12:12:33 +01:00
parent e1695a56c4
commit 1e0d9ddb20
1 changed files with 24 additions and 31 deletions
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55
lib/Analysis/ValueTracking.cpp
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@ -617,6 +617,29 @@ bool llvm::isValidAssumeForContext(const Instruction *Inv,
// feeding the assume is trivially true, thus causing the removal of
// the assume).
if (Inv->getParent() == CxtI->getParent()) {
// If Inv and CtxI are in the same block, check if the assume (Inv) is first
// in the BB.
if (Inv->comesBefore(CxtI))
return true;
// Don't let an assume affect itself - this would cause the problems
// `isEphemeralValueOf` is trying to prevent, and it would also make
// the loop below go out of bounds.
if (Inv == CxtI)
return false;
// The context comes first, but they're both in the same block.
// Make sure there is nothing in between that might interrupt
// the control flow, not even CxtI itself.
for (BasicBlock::const_iterator I(CxtI), IE(Inv); I != IE; ++I)
if (!isGuaranteedToTransferExecutionToSuccessor(&*I))
return false;
return !isEphemeralValueOf(Inv, CxtI);
}
// Inv and CxtI are in different blocks.
if (DT) {
if (DT->dominates(Inv, CxtI))
return true;
@ -625,37 +648,7 @@ bool llvm::isValidAssumeForContext(const Instruction *Inv,
return true;
}
// With or without a DT, the only remaining case we will check is if the
// instructions are in the same BB. Give up if that is not the case.
if (Inv->getParent() != CxtI->getParent())
return false;
// If we have a dom tree, then we now know that the assume doesn't dominate
// the other instruction. If we don't have a dom tree then we can check if
// the assume is first in the BB.
if (!DT) {
// Search forward from the assume until we reach the context (or the end
// of the block); the common case is that the assume will come first.
for (auto I = std::next(BasicBlock::const_iterator(Inv)),
IE = Inv->getParent()->end(); I != IE; ++I)
if (&*I == CxtI)
return true;
}
// Don't let an assume affect itself - this would cause the problems
// `isEphemeralValueOf` is trying to prevent, and it would also make
// the loop below go out of bounds.
if (Inv == CxtI)
return false;
// The context comes first, but they're both in the same block.
// Make sure there is nothing in between that might interrupt
// the control flow, not even CxtI itself.
for (BasicBlock::const_iterator I(CxtI), IE(Inv); I != IE; ++I)
if (!isGuaranteedToTransferExecutionToSuccessor(&*I))
return false;
return !isEphemeralValueOf(Inv, CxtI);
return false;
}
static bool isKnownNonZeroFromAssume(const Value *V, const Query &Q) {